The present invention relates to plastic fittings and, more particularly, to plastic fittings for creating a sealed and enclosed environment around the pre-flared end of a section of plastic tubing.
Numerous industries use tubing and fittings of fluoroplastics, e.g., polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA), and other synthetic resins, for the transfer of various fluids in extreme temperatures and conditions. These fluoroplastic fittings offer extraordinary corrosion resistance and high purity which make the materials ideal for the semiconductor processing industry. However, such plastic fittings and tubings, in that they are made of plastic rather than traditional materials such as stainless steel, bronze and copper, do not have the rigidity and strength of conventional fittings. Thus particular connection configurations that may work very well with metal fittings and metal tubing, do not work adequately when made from fluoropolymer materials. To maintain a clean and non-hazardous process it is essential that the fittings provided for coupling sections of tubing are not easily disconnected and that the integrity of tubing/fitting interface is maintained. Various types of fluoropolymer fittings have been provided for these purposes.
One standard type of fitting known as FLARETEK(copyright) fitting, available from the assignee of this application, provides for a fitting body, having a nose with a rounded tip and cylindrical section, and a threaded portion at the base of the nose. A fitting nut is typically placed on the tubing before the tubing end is flared. The end portion of tubing with the flared end is placed over the nose section and the fitting nut is slid over and secured to the fitting body axially compressing the flared end on the nose by the collar of the nut creating a seal between the inside surface of the tubing and nose. When assembled the nut extends completely over the flared section. The seal is created around the substantially cylindrical nose but is principally at the tip of the nose. In these fittings, the inside diameter of the flared section is slightly greater that the outside diameter of the non-flared portion of the tubing. The tubing flare forms an exaggerated s-shape with the flared section axially extending and having a constant diameter. The flare is formed by heating the end of the tubing and expanding same on an appropriately shaped form.
Such flared fitting bodies have the nose portion including the portions which seal exposed when they are unassembled subjecting the fitting bodies to potential damage. Similarly, the exterior threads are also exposed subjecting them to possible damage. However in certain applications it would be desirable to have a flared fitting that offers further advantages such as additional secondary sealing, a fitting in which the sealing surfaces of fitting body are not exposed when the fitting is unassembled, and moreover that provides more protection to the sealing components when assembled.
A plastic fitting couples a section of tubing with a concave flared end to a fitting body. In a preferred embodiment, the flared tube has an expanded s-shape in the cross-section and the plastic fitting generally comprises a fitting body and a fitting nut. The fitting body includes an internal nose section having a curvilinear sidewall and a cylindrical surface that have been preformed to substantially match in shape the flare of the tubing. In a preferred embodiment, the nut has external threads that engage internal threads on the fitting body. The fitting nut is threadably coupled to the fitting body and includes a flare-engaging collar which secures the flared end of the tubing to the fitting body through a circumferential point contact. Additional securement of the tubing is provided by an axially inset annular converging recess, proximate the tapered nose section, which defines a seat sized to receive the end edge of the tube.
During assembly, the flared end of the tubing with the fitting nut thereon is placed over the nose section of the fitting body. The fitting nut is rotated and drawn towards the fitting body by virtue of interfacing threads. As the fitting nut is drawn closer to the fitting body, the flare-engaging collar operates to axially compress the flared end of the tubing on the nose as well as axially seat the edge portion of the flared end into the axially inset converging annular seat.
Both the fitting body and fitting nut are designed for easy grasping and, thus, assembly of the plastic fitting. The fitting body is preferably provided with one or more planar surfaces for easier grasping while the fitting nut is preferably provided with a number of winged extensions for easier grasping. The fitting body may be integral or part of a component or device, such as a valve, or may have connection means such as external threads, another flared end fitting, or a flange.
A feature and advantage of the invention is that redundant sealing connections are provided. The flared end of the tubing seals against the curvilinear portion of the tapered nose as effected by the tightening of the nut. The flared end also seals against the cylindrical surface of the tapered nose. This sealing is not directly dependant upon the tightness of the nut in the fitting. Additionally, in a preferred embodiment, the tip of the flared end seals into a converging annular recess.